handleRequestMessage

Subclasses must implement this method to handle the request Message. The return
value may be a Message, a MessageBuilder, or any plain Object. The base class
will handle the final creation of a reply Message from any of those starting
points. If the return value is null, the Message flow will end here.

setExpectSingleResult

public void setExpectSingleResult(boolean expectSingleResult)

This parameter indicates that only one result object shall be returned from
the Stored Procedure/Function Call. If set to true, a resultMap that contains
only 1 element, will have that 1 element extracted and returned as payload.
If the resultMap contains more than 1 element and expectSingleResult is true,
then a MessagingException is thrown.
Otherwise the complete resultMap is returned as the Message payload.
Important Note: Several databases such as H2 are not fully supported.
The H2 database, for example, does not fully support the CallableStatement
semantics and when executing function calls against H2, a result list is
returned rather than a single value.
Therefore, even if you set expectSingleResult = true, you may end up with
a collection being returned.